1. What is a moral intuition?
According to McMahan:
[It] is a spontaneous moral judgment, often concerning a particular act or agent, though an intuition may also have as its object a type of act or, less frequently, a more general moral rule or principle. In saying a moral intuition is a spontaneous judgment, I mean that it is not the result of conscious inferential reasoning. In the first instance at least, the allegiance the intuition commands is not based on an awareness of its relations to one's other beliefs. If one considers the act of torturing the cat, one judges immediately that, in the circumstances, this would be wrong. One does not need to consult one's other beliefs in order to arrive at this judgment. This kind of spontaneity, I should stress, is entirely compatible with the possibility that a fair amount of cognitive processing may be occuring beneath the surface of consciousness (pp. 93-94).
2. There is not a special organ or faculty that perceives moral facts.
Although some have held that ethical intuitions are the deliverances of a special organ or faculty of moral perception, typically understood as something like an inner eye that provides occult access to a noumenal realm of objective values (p. 94), I reject this notion. I don't believe that there is something like a sixth sense that is able to perceive moral facts.
3. Intuitions are not infallible.
4. Intuitions are biologically based.
But numerous considerations--such as the diversity of moral intuitions, the fact that people do often doubt and even repudiate certain of their intuitions, and the evident origin of some intutitions in social prejudice or self-interest--make it untenable to suppose that intuitions are direct and infallible perceptions of morality (pp. 94-95).
5. Intuitions may differ among people.
One piece of evidence for this is the surprising uniformity of our intuitions about particular cases. We have been impressed for so long by the claims of anthropologists, English professors, undergraduates, and others about the diversity of moral opinion that we are inclined to overlook how much agreement there actually is. Interestingly, what one finds is that moral disagreements tend to widen and intensify the more we abstract from particular cases and focus instead on matters of principle or theory. When the partisans of different schools of moral thought turn their attention to particular cases, there is far more intuitive agreement that their higher-level disputes would lead one to suspect (pp. 106-07).
There are several explanations for this. One is that our moral intuitions undoubtedly stem from numerous diverse sources: while some derive from biologically programmed dispositions that are largely uniform across the species, others are the products of cultural determinants, economic or social conditions, vagaries of individual character and circumstance, and so on. Given the heterogeneity of these sources, it is hardly surprising that there are conflicts (p. 109).